Phone, camera, Laptop, laptop case/cover, good quality backpack, chargers & adapters for each place you are going (or a universal adapter), noise cancelling headphones, shower shoes, padlock.

I also prefer to have the following, but wouldn’t say they’re a must: your own pillow case, ear plugs (if you are staying in hostels or noisy cities), poncho, travel journal (fun to write about the places you go or have new friends sign it along the way!)